The present invention relates to a magneto-optical recording medium including a vertical magnetic-anisotropic magnetic film layer comprising a ferrimagnetic oxide which is not deteriorated by oxidation, allowing recording of information or data and reproducing the same by application of laser beams.
Conventionally, many magneto-optical recording mediums for recording and reproducing information by application of laser beams thereto have been proposed, which comprise amorphous magnetic alloy films consisting of alloys of transition metals such as Fe and Co and heavy rare earth metals such as Tb, Gd and Dy. However, in these amorphous magnetic alloy films, the heavy earth metals are so easily oxidized that, in the presence of water, the magnetic characteristics of the magnetic alloy films are considerably deteriorated due to the oxidization thereof. In order to prevent such deterioration of the magnetic alloy films, there has been proposed a protective layer for protecting the magnetic alloy films, which protective layer comprises an oxide such as SiO.sub.2, SiO and TiO.sub.2, or a nitride such as TiN and SiN. Such protective layer has to be free from pin holes. However, it is extremely difficult to prepare a protective layer without any pin holes.
Furthermore, when producing a magnetic film layer comprising a substrate and a magnetic film formed thereon, a large amount of oxygen contained in the chamber for producing the magnetic film is adsorbed at the interface between the substrate and the magnetic film layer, and the adsorbed oxygen reacts with the heavy rare earth metal contained in the magnetic film, forming a heavy rare earth metal oxide, by which the magnetic film is considerably deteriorated.
At the time of recording, the recording medium is heated for a long period of time, and by the application of heat, the magnetic characteristics of the recording medium are deteriorated with time. Due to the above-mentioned adverse factors, it is difficult to produce a magneto-optical recording medium comprising a magnetic layer consisting of a transition metal--heavy rare earth metal alloy that can be used for 10 years or more.
In order to prevent the oxidization of the magnetic layer, an anti-oxidation layer is necessary, but the use of an anti-oxidization layer not always practical in the production of the recording medium, because the layer structure of the recording medium becomes complex if an anti-oxidation layer is included, and the production of the recording medium becomes difficult.
When plastics are employed as the materials for the substrate of the recording medium, a technique for eliminating the moisture-penetration properties of the plastics is required.
A hexagonal-system M-type ferrite has been investigated for use as a magnetic bubble material as being a magnetic material free from deterioration by oxidation. This material, however, has a curie temperature as high as 450.degree. C. or more. Therefore, it cannot be used as a magneto-optical recording material for recording by application of laser beams thereto.